European patent EP 792 692 B1 discloses a high pressure nozzle for descaling steel products, which is provided with a jet director within a supply channel to a discharge opening. The jet director is formed in a cross-sectionally radial component and has a cylindrical central part from which extend radially flow guidance surfaces. To reduce the flow resistance of the jet director, in both the upstream and downstream directions the cylindrical central part is extended in the form of a conical tip. Upstream of the jet director is located a filter, which is formed from a tubular portion with a spherical cap-shaped termination and with radial grooves for the entry of liquid. The radial grooves extend into the spherical segmental cap of the filter. Downstream of the jet director there is a gradual tapering of the flow channel, which extends with decreasing taper angle to a discharge chamber in a mouthpiece. The mouthpiece has the discharge chamber and the discharge opening connecting onto said discharge chamber. As a result of the very high liquid pressures with which the high pressure nozzles are operated for descaling steel products and which can be several 100 to 600 bar, a low flow resistance is decisive, because pressure losses within the high pressure nozzle either lead to a lower removal or to the need for a higher pressure of the supply line. In addition, the shape of the flat jet or spray produced is decisive and for achieving an excellent removal action it should have a minimum width. Finally the high pressure nozzle is exposed to considerable mechanical stresses, because e.g. pressure surges in the supply line can lead to a collapse of the high pressure nozzle filter.
The invention aims to provide an improved high pressure nozzle.
According to the invention for this purpose is provided a high pressure nozzle, particularly for descaling steel products, which has a jet director within a supply channel to a discharge opening, in which in an area directly surrounding the median longitudinal axis of the supply channel the jet director has a free flow cross-section.
This leads to a so-called coreless jet director, which is characterized on the one hand by a low flow resistance and on the other by a very good orienting or straightening action. Thus, the jet director has a flow channel, without built-in fittings, directly surrounding the median longitudinal axis. Compared with conventional jet directors having a central, cylindrical component from which flow guidance surfaces emanate radially, the inventive jet director has a significantly reduced flow resistance, because the flow channel directly surrounding the median longitudinal axis of the supply channel remains free and can be used for an unhindered through-flow. As the free cross-section available for the flow is much larger, a significant flow resistance reduction is obtained. The free flow cross-section can e.g. have a radius amounting to approximately ⅕ of the internal radius of the jet director.
According to a further development of the invention the jet director has flow guidance surfaces extending parallel to and towards the median longitudinal axis of the supply channel.
By means of such flow guidance surfaces oriented parallel to the median longitudinal axis of the supply channel a good directivity of the jet director can be obtained and a flow which has traversed the jet director is oriented substantially fully parallel to the median longitudinal axis downstream of the jet director.
In a further development of the invention the flow guidance surfaces extend radially towards the median longitudinal axis.
This leads to planar, flow guidance surfaces having a very good orienting action with a low flow resistance.
In a further development of the invention a tapering of the supply channel takes place downstream of the jet director.
Such a tapering or narrowing concentrates the flow and over a short path the flow channel can be reduced to the cross-section of the discharge chamber. According to the invention there is a short taper and the tapering portion of the supply channel only has roughly half to a third of the jet director length.
In a further development of the invention, downstream of the jet director is connected to the taper a portion having a constant cross-section, which passes into a tapering discharge chamber.
By means of such a constant cross-section portion a flow calming can be brought about, which leads to a very good jet quality with a low flow resistance. The constant cross-section portion is advantageously longer than the taper downstream of the jet director. It has proved to be advantageous for the constant cross-section portion to be at least twice as long as the taper downstream of the jet director and in particular to make it seven times as long as the taper. The discharge chamber passes into the discharge opening from which emanates the spray jet.
In a further development of the invention upstream of the jet director is provided a filter having entrance slots oriented radially to the median longitudinal axis. Advantageously the entrance slots extend parallel to the median longitudinal axis. The filter can have a spherical segmental filter cap provided with entrance openings parallel to the median longitudinal axis.
The entrance openings in the spherical segmental filter cap are separated from the entrance slots, so that the spherical segmental filter cap can have a very stable construction and can in particular withstand any pressure surges occurring in the supply lines. The filter cap e.g. has a circumferential collar ensuring a high mechanical strength. The entrance slots in the filter consequently terminate upstream of the spherical segmental filter cap.
In a further development of the invention end boundary surfaces of the entrance slots located on the side of the jet director are rounded or inwardly inclined, the rounded end boundary surfaces having a convex construction towards the median longitudinal axis. The bottom of the entrance slots which, in the flow direction, is located on the side of the jet director is consequently outwardly curved or convexly constructed towards the median longitudinal axis. Alternatively the slot bottom is inclined inwards and is in particular conical shell section-like, the cone tapering in the flow direction. Thus, the flow through the entrance slots is gradually deflected towards the median longitudinal axis in the vicinity of the slot bottom. This significantly reduces turbulence in the vicinity of the slot bottom and there is a low flow resistance and a flow oriented substantially parallel to the median longitudinal axis downstream of the jet director.
In a further development of the invention the filter is formed by means of a filter cap and a main filter part, the filter cap and main filter part being manufactured as single components and then permanently interconnected.
This facilitates the manufacture even of geometrically complicated shapes in the vicinity of the filter cap and main filter part. Following the permanent connection of filter cap and main filter part a stable, flow-favourable filter unit is provided.
In a further development of the invention the filter cap and main filter part are manufactured by metal powder die casting and are then sintered together.
Metal powder die casting makes it possible to produce geometrically complicated shapes, which could not be produced by mechanical working or could only be produced when involving significant effort and expenditure. This e.g. includes the convex construction of the end faces of the filter entrance slots oriented towards the median longitudinal axis. Conventionally such entrance slots are constructed by immersing a milling cutter or saw blade in a tubular component. This generally leads to an outwardly directed, concave construction of the end faces, which is hydraulically unfavourable.
In a further development of the invention the main filter part is provided with the jet director.
This makes it possible to provide a low flow-resistance combined jet director and filter component. When manufacturing said combined jet director and filter component by means of metal powder die casting the inventive coreless jet director and a flow-favourable construction of the entrance slots on the filter can be implemented and manufactured serially. Alternatively the jet director can also be constructed as a separate flow channel component or can be integrated into a different nozzle component to the filter.
In a further development of the invention the filter cap has a circumferential collar with radially inwardly extending projections, which engage in matching recesses of the main filter part.
This makes it possible to implement a very stable connection of the filter cap to the main filter part, which also allows a very flow-favourable construction. Alternatively the main filter part can be provided with a circumferential collar with radially inwardly or outwardly extending projections, which then engage in matching recesses of the filter cap. Independently of whether the circumferential collar is provided with radially extending projections on the filter cap or the main filter part, the inventive advantages of a very stable, flow-favourable construction of the connection between filter cap and main filter part can be achieved.
In a further development of the invention the main filter part is provided on its end adjacent to the filter cap with webs extending parallel to the median longitudinal axis and between which the recesses are formed. Advantageously the entrance slots are formed between the main filter part webs.
Thus, the main filter part has circumferentially distributed quantities of fingers or webs extending in the upstream direction and between which the entrance slots are formed. The ends of said webs are received and fixed by the filter cap. Following the permanent connection of the main filter part and filter cap this leads to a stable component. With particular advantage the filter cap and main filter part can be manufactured by metal powder die casting and then sintered together.
The problem of the invention is also solved by a method for the manufacture of a spray nozzle, particularly a high pressure nozzle for descaling steel products, in which the following steps are provided:
mixing metal powder with plastic binder,
die casting the resulting mixture in a mould,
removing the binder by chemical and/or thermal processes and sintering the intermediate product obtained after removing the binder.
Such a metal powder die casting method also makes it possible to achieve very complicated geometrical shapes, which cannot be manufactured or can only be manufactured with considerable effort and expenditure by conventional mechanical working. The use of die casting machines makes it possible to bring about comparatively inexpensive manufacture in series production quantities, which reduces costs, e.g. compared with precision casting. It has surprisingly been found that components obtained by metal powder die casting are sufficiently stable to withstand the significant operating pressures of several hundred bar occurring with high pressure nozzles for descaling steel products. Over and above the high operating pressures, in pipelines for supplying descaling nozzles pressure surges can occur which are a multiple of the operating pressures. Metal powder die casting leads to sintered components and it is initially to be expected that the sintered components would have a brittle character and would therefore be unsuitable for loads with extreme pressure peaks, such as occur when operating descaling nozzles. However, tests have surprisingly shown that the sintered parts obtained by metal powder die casting and in the case of a corresponding design are able to withstand these loads and stresses and also offer new possibilities for the flow optimization of high pressure nozzles.
According to a further development of the invention the individual components in the form of intermediate products are assembled following binder removal and then the assembled intermediate products are sintered.
As a result components can be manufactured integrally, e.g. in the form of a combined jet director and filter component including the filter cap, because following sintering the assembled intermediate products are permanently interconnected. This offers further possibilities for a simultaneously stable and flow-favourable design of high pressure nozzles. Following binder removal the intermediate product has a comparatively fragile structure, because following binder removal the metal powder has a porous structure. Only during sintering is the intermediate product compacted and is then mechanically highly loadable.
In a further development of the invention the metal powder at least partly contains hard metal powder.
It has surprisingly been found that even hard metal/carbide parts can be manufactured by metal powder die casting. This is particularly advantageous for the manufacture of mouthpieces of high pressure descaling nozzles. Also in the mouthpiece area and specifically in the area of the discharge chamber and discharge opening this makes it possible to bring about complicated geometrical shapes, which cannot or cannot be produced with acceptable costs by mechanical working. Following sintering of the hard metal powder intermediate product a hard metal component is obtained, which is eminently suitable for use as a high pressure descaling nozzle mouthpiece and in particular has a long service life.
In a further development of the invention the high pressure nozzle has at least one filter and a jet director in a combined filter and jet director component, which is assembled from at least two individual parts, which are permanently interconnected by sintering.